Repairing Baby Swing - Circuit Board Assistance

Thread Starter

Maverick3324

Joined Nov 25, 2018
1
Disclaimer: I have very minimal experience and knowledge working with circuit boards, but wanted to give fixing this swing one last go before I throw in the towel and toss it. I have already searched the forums for baby swing repairs and none of the previous threads were able to directly answer my question. Thank you in advance for your time and help!

My son's baby swing stopped swinging about a year ago, he was getting too big, but we had another little one on the way so I wanted to try and fix it. Everything else on the swing worked fine (music, mobile, LEDs, etc.). I took it apart and found that the worm gear on the motor wasn't catching the threads probably in the gearbox and that prevented it from swinging. I re-seated the motor and everything was fine and dandy and the swing worked great. I originally thought the motor had gone bad, so I had ordered a new motor and kept it for back-up if the motor ever did go bad.

Fast forward to earlier this week and the swing stopped swinging again. Music, mobile and LEDs still work great, but no swinging action. I took it apart again and found that the motor didn't turn on at all when you click the increase speed button. I put the new motor in and got nothing. I then tested the motors with a 9V battery and BOTH motors still function fine when tested on a 9V. Given this information, I think the issue has something to do with the circuit board. I have included pictures of the board below. I took off the transistor heat sink to examine the area for scorches and couldn't find anything noticeable. Any other ideas on what might be going wrong here? Is the next logical step to replace the transistor? Thank you all in advance for your time and help!
20181125_165047.jpg 20181125_165150.jpg 20181125_165200.jpg 20181125_165835.jpg
 

wayneh

Joined Sep 9, 2010
17,496
You could try removing Q2 for testing off board, or just replace it. It could certainly have failed with no indication by its appearance. Electrolytic capacitors are known to fail with age, so if you need to order the transistor I’d add those to the order. They’re less likely the problem than the transistor, in my opinion, but they are a question mark. They’re cheap and not too hard to replace.

Without a schematic and some test equipment (like an oscilloscope), it can be pretty tough. Once the transistor is out, you might check that the base voltage changes when the motor should come on.
 

efenimor

Joined Aug 10, 2023
2
@wayneh
You could try removing Q2 for testing off board, or just replace it. It could certainly have failed with no indication by its appearance. Electrolytic capacitors are known to fail with age, so if you need to order the transistor I’d add those to the order.
Hello - I'm having similar problem to original post. I have disassembled my swing and found a burnt Q2 component. I'm not a circuit person, I have no experience identifying circuit components, I had to register for this site just to be able to post this message. I am a proficient solder-er thought so I'm confident I can replace the burned component if I can identify a suitable replacement. I'm hoping you might be able to help me identify and source a replacement Q2 component. The markings on it are "K MPS 8550D 845".

Can you adivse if there are any standard household electronics you would expect to contain a suitable replacement or substitute I might be able to scavenge from? Otherwise, where would you go about ordering one online? It looks like all the radio-shacks near me are now closed, are there any typical brick and mortar stores that carry this sort of thing anymore?

Thanks for any help you can provide. Regards, Eric.
 

wayneh

Joined Sep 9, 2010
17,496
Agree on Q6. I can't see now what I was thinking back then when I referenced Q2. My guess is I simply got the number wrong. I can't even seem to find a Q2 in the pictures. Anyway that "big" transistor Q6 is obviously meant to handle more power than anything else on the board and that makes it a top suspect. It's also something that can be replaced, unlike that black blob for instance.
It's probably this: https://pdf1.alldatasheet.com/datasheet-pdf/view/70001/KEC/MPS8550.html
I wouldn't worry about finding that exact part. You need to match (or exceed) the voltage and amperage specs, and having the same pinout would be best. In my estimation this is not a high-frequency application or anything odd where the fine points in the specs might matter. It's a power switch to drive the motor and any sufficiently beefy PNP transistor ought to be fine. My 2¢.
Brick and mortar suppliers are virtually gone. I use Mouser, Newark, Digi-Key and even Amazon, the latter with caution. There are a lot of counterfeits out there.
My earlier comments about the capacitors still stand. As long as you're placing an order, adding a few caps will be very inexpensive and they won't take long to remove and replace.
 
Last edited:

efenimor

Joined Aug 10, 2023
2
@sagor @wayneh - First off, let me say thank you for even replying to my question on a very old thread, especially when I acknowledged I know very little about circuits and therefore not likely to solve any problems for you in return. A side note that I have a different model fisher price swing than the original poster - Fisher Price Cradle n Swing My Little Lamb - and therefore my PCBs are laid out differently, with different components (i.e. the Q6 does exist on my board).

Secondly, wanted to report and document for others that I did successfully repair my swing using the advice above. I ended up replacing a known burned Q6 transistor, an adjacent capacitor that had its case minorly damaged by the thermal burn up of the Q6 transistor, and the main motor driver Q2 transistor which had no signs of damage but was cheap to replace. Parts used documented below, purchased from Mouser.com. As stated by commenters above, the shipping price is more than the price of the components, order extra.

I would have loved to replace the components 1 at a time to know which one(s) was really the failure point, however that would have taken more time than I have at the moment (newborns).

Photos below as well.

Thanks again to @sagor and @wayneh for your help. Baby girl is sleeping soundly in her swing now as I type this.

Line Number​
Mouser Part Number
Customer Part Number
Manufacturer Part Number
Description​
Requested
Delivery
Date(s)​
Estimated
Shipment
Date(s)​
Quantity​
Unit Price
(USD)​
Extended Price
(USD)​

1​
RoHS
Small Transistor Q6 from the Fisher Price Swing


512-SS8550DBU
SS8550DBU
TO92 PNP 2W BULK​
AUG 11, 2023​
AUG 11, 2023​
1​
0.450​
0.45​
2​
RoHS
Big Transistor Q2 from the Fisher Price Swing


511-MJE3055T
MJE3055T
NPN Gen Pur Switch​
AUG 11, 2023​
AUG 11, 2023​
2​
1.140​
2.28​
3​
RoHS
Capacitor from the Fisher Price Swing - 10V 1000uF


232-10PK1000MEFC8X15
10PK1000MEFC8X11.5
GENERAL PURPOSE ELEC​
AUG 11, 2023​
AUG 11, 2023​
2​
0.440​
0.88​

IMG-0210.jpgIMG-0216.jpg
 
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